Chlorine dioxide is extensively used as a bleach chemical for wood pulps and may be formed by a variety of processes. Most large scale commercial operations are based on reduction of sodium chlorate in an aqueous acid reaction medium. The chlorine dioxide usually is dissolved in water and is used as an aqueous solution.
Chlorine usually is coproduced with the chlorine dioxide, either as a result of the employment of added chloride ions as the reducing agent or as a result of inefficiencies in the chlorine dioxide generating process.
It often is desirable to provide an aqueous chlorine dioxide solution which is substantially chlorine free, for example, in pulp bleaching operations where a high proportion of chlorine dioxide is required. Prior proposals for the separation of chlorine from aqueous chlorine dioxide solutions have involved selective stripping procedures, as described in U.S. Pat. No. 3,854,901 (E121), assigned to the assignee hereof.